The vehicles driven by an internal combustion engine continuously emit particulate matter and nitrogen oxides which are major reasons of pollutions, therefore the environmental regulations on the exhaust gas of the vehicles have been strengthening.
As a method for removing the pollutants, an effort to decrease the emission of pollutants in advance by maximizing the efficiency of engines and upgrading fuels. As well as researches on post-cleaning of exhaust gas such as a filter for removing particulate matter and a catalyst for abating nitrogen oxide haven been conducted.
However, a process for post-cleaning exhaust gas in the above efforts is dependent on the state of vehicles and their driving conditions a lot, therefore the condition to which this method is applied are greatly limited.
The plans for utilizing a heat by an electric heater or a burner as an energy source for regenerating filters are currently tried but the limited power and a space required for establishing an external burner should be overcome so that it is applied to the system.
Recently, a plurality of patent applications to convert hydrocarbon into a combustable reduced gas for applying to the vehicle have been filed, but could not suggest a concrete system configuration required for combustion and reformation.
If hydrocarbon is sprayed into the exhaust gas in the condition of the low temperature of the exhaust gas, a recondensation should proceed with a temperature below the boiling point of a light oil, So additional heating devices for the exhaust gas should be mounted for preventing the recondensation.
In an effort to supplement the above, a method has been suggested to transfer the light oil into vapors by using a vaporizer driven by electricity, and mixing it with the exhaust gas to combust it on DOC (Diesel Oxidizing Catalyst).
However, it is impossible to combust the vaporized diesel below than 235° C. in DOC, and the periods for spraying fuels are limited because it is necessary to prepare for recondensations of the fuels vaporized due to a low temperature of the exhaust gas.
FIG. 1 is a general configurational view for heating DPF (Diesel Particulate Filter) (12) by spraying fuels. A vaporized fuel with heat source is mixed with an exhaust gas generated from the engine (100) and is introduced into the DOC (11). The exhaust gas and fuel are oxidized in the DOC (11) to generate heat which can be used as a heat source so that the DPF (Diesel Particulate Filter) (12) is reproduced.
The DOC (11) is served for combusting a fuel which is supplied to SOF (Soluble Organic Fraction) and DPF (Diesel Particulate Filter) in carbon monoxide, hydrocarbon and particulate matters which is contained in exhaust gas.
The DPF (12) has a configuration to be disposed in serial at the rear end of the DOC, and collects the particulate matter in exhaust gas to keep the particulate matter from being released. If more than a predetermined amount of the particulate matter is collected, they are combusted and regenerated by a heat supplied from a supplementary heat energy source.
In FIG. 1, the heat generated from the DOC (11) is used.
In FIG. 2, a fuel vaporizing device (21) is further comprised in comparison with FIG. 1, and supplies the vaporized fuel (especially, a light oil) to an exhaust gas stream to improve the mixing it with the exhaust gas, functioning as promoting oxidation in the DOC (22).
The collected particulate matter by DPF (made of metal or ceramic material), especially in a diesel vehicle, is oxidized continuously or is combusted periodically to regenerate the filter.
The period for regenerating the filter has a variation in accordance with a NOx/soot ratio and temperature distributions of exhaust gas. The temperature of exhaust gas is subjected to vehicle models, engine types, road situations and traffic conjestions etc. and the Nox/soot rate is also variable in accordance with an EGR rate.
In other words, it is impossible to change the driving conditions of an engine in a vehicle on the road so as to control the temperature of an exhaust gas in consideration of capacities of a post-cleaning device, and we need a supplementary heating system for heating exhaust gas.